Inkjet printing has gained popularity in a number of applications. One of the growing printing applications is printing of billboards, banners and point of sale displays. The ink-jet printing process involves manipulation of drops of ink ejected from an orifice or a number of orifices of a print head onto an adjacent print medium or substrate. An ink-jet print head consists of an array or a matrix of ink channels or cavities each ending by an orifice or nozzle. The nozzles of an array or a matrix of ink channels are typically made on a common substrate called nozzle or orifice plate. Usually, one of nozzle plate surfaces is attached to an array or a matrix of ink channels in a way that each nozzle faces a corresponding ink channel. The other surface “open” surface faces the printed media or substrate. Each nozzle selectively ejects ink droplets in the direction of the printing substrate. A given nozzle of the print head ejects the ink droplet in a predefined print position on the media. An assembly of the adjacently positioned on the media ink droplets creates a predetermined print pattern or image. Relative movement between the media or substrate and the print head enables printing substrate coverage and image creation. The selection of printing media is large and varies from paper and fabric to metal and glass.
The quality of the print produced by an ink jet printer to a large extent depends on the state of the nozzle plate and especially the surface of the nozzle plate. Dry and free of debris nozzle plate surface enables accurate droplet placement reducing droplet position caused printing artifacts. It is however, difficult to maintain the nozzle plate surface dry and free of debris. Ink mist formed during droplet ejection process resides on the nozzle plate surface; dust, paper and fabric lint remain on the nozzle plate surface. When printing is performed with UV curable ink, ink mist and residue might be cured by stray light on the nozzle plate surface. Although different coatings to reduce nozzle plate surface wetting and static attraction have been developed only repetitive and frequent nozzle plate surface cleaning helps to maintain correct operating status of the nozzle plate.
There is a number of techniques developed for cleaning of the “open” or facing the printed media nozzle plate surface. Some of these techniques relay on a simple wiping process, where a soft blade, such as one made of fluoro-silicone wipes the nozzle plate surface periodically. This operation wipes out debris and excess ink from the nozzle plate surface returning it to the original dry and free of debris state. The drawback of this technique is that debris and excess ink can contaminate some of the nozzles during the wiping step. Moreover residual ink located on the soft blade may contaminate the nozzle plate surface and therefore lead to a result opposite to what was expected.
The soft blade wiping method is not applicable to print heads operating with UV curable ink. Often UV curable ink residue always present on the soft blade cures or is in process of curing becoming a hard body. Wiping nozzle plate surface with a blade having on it cured ink particles not only scratches the nozzle plate surface, it contaminates the nozzle plate and clogs the nozzles making the print head unusable.
Another method of wiping is by a cloth wetted in a cleaning solution. The cloth is rolled from a roller-to-roller and thus avoids nozzle plate surface contamination, however lint and hard particles that are present in the debris may scratch the nozzle plate surface and damage the anti-wetting coating.
Methods of non-contact cleaning by a stream of fluid are also known in the art. U.S. Pat. No. 4,970,535 to Oswald et al., discloses an ink jet print head face cleaner that provides a controlled air passageway through an enclosure formed against the print face. Air is directed through an inlet into a cavity in a body. The body has a face with an opening into the cavity. This face is sealingly placeable against the print face. The cavity has a limited size so that air is directed without interruption through the cavity past the ink jet apertures, and out an outlet. The cleaner body is coupled resiliently to a platform to allow positioning of the body and print faces flush with each other. A vacuum source is preferably attached to the outlet to create a sub-atmospheric pressure in the cavity to further seal the two faces together. A collection chamber and removable drawer are positioned below the outlet to facilitate disposing of removed ink.
The fluid stream is oriented along the nozzle plate and moves ink residue from one end to another. There always exist a possibility that some residue will be trapped in a nozzle and clog it. Use of vacuum and sealed compartment increases the cost of the solution.
U.S. Pat. No. 6,196,657 to Hawkins et al. discloses a multi-fluidic cleaning for an ink jet print head and a method for assembling the same. The print head has a surface defining at least one orifice there through the at least one orifice being susceptible to being obstructed by contaminants. A cleaning assembly of the invention is disposed proximate the surface for directing a flow of fluid along the surface and across the at least one orifice to clean contaminants from the surface and the at least one orifice. The cleaning assembly includes a cup sealingly surrounding the at least one orifice, the cup defining a cavity therein. The cleaning assembly further includes a valve system in fluid communication with the cavity for allowing a fluid flow stream consisting of alternating segments of at least one liquid cleaning agent from a liquid cleaning agent source and another element such as a gas from a gas source or a second liquid cleaning agent from a liquid cleaning agent source into the cavity.
Hawking also requires creation of a sealed compartment that increases the cost of the solution. The fluid stream is oriented along the nozzle plate and moves ink residue from one end to another. There always exist a possibility that some residue will be trapped in a nozzle and clog it.
U.S. Pat. No. 5,184,147 to MacLane et al discloses an ink jet print head cleaning and maintenance system that has a purge chamber for applying a vacuum to a nozzle orifice surface. A specialized baffle diverts ink entering the purge chamber away a vent port through which the vacuum is drawn. An elongated wipe engages and wipes the orifice surface and is preferably moved at an extremely slow rate across the surface to enhance the wiping operation. An air knife directs a narrow stream of air across a portion of the nozzle orifice surface with air from the air stream being scanned across the surface for cleaning purposes. A specialized drip edge is positioned beneath the orifice surface for directing drops of ink away from the ink jet print head, the drops of ink being generated during the cleaning procedures. A mechanically simple cam mechanism coupled to a rotatable drum of the printer may be used to shift the maintenance system against the nozzle orifice surface for cleaning purposes.
The system however, requires a special mechanism for scanning the air stream across the surface for cleaning purposes. The cleaning system itself requires a positioning mechanism, although a simple one, to be employed for placing in a working position and returning to a idle state.
U.S. Pat. No. 6,497,472 to Sharma et al. teaches a print head that comprises a print head body defining an interior chamber and an orifice plate. The orifice plate has an outer surface and further defines a cleaning fluid orifice through the orifice plate for conducting a flow of a cleaning fluid through the cleaning fluid orifice and onto an outer surface of said orifice plate. The orifice plate also defines a drain orifice for conducting a flow of cleaning fluid from the surface to the interior chamber. A supply of pressurized cleaning fluid is disposed in said cavity and connected to the cleaning fluid passageway. During cleaning operations, the fluid flow system defines a flow of a cleaning fluid from the passageway and onto said outer surface. The drain orifice receives cleaning fluid from the outer surface and channels the cleaning fluid into the fluid return.
Sharma discloses that all print head facilities are part of the print head and accordingly the cost of the print head is increased. Special sealed compartment through which the cleaning solution flows is temporarily created for the cleaning process.
Therefore, there is a need in the industry in for a method of non-contact, ink jet print head nozzle plate surface cleaning solution. A solution that would provide nozzle plate cleaning without mechanical contact between the nozzle plate and the cleaning tool and would not require manual interference.
All of the above mentioned print head cleaning methods and devices are adapted to clean only one print head at a time. Most of the present ink jet printing system is printing with a block of print heads, where a number of print heads print the same color. This enables the printers of getting a higher throughput and high printed image density. The prior art solutions do not suggest a method of non-contact or contact simultaneous (parallel) cleaning of all print heads.
There is also a need in the industry for a cleaning solution that would not contaminated by the cleaning fluid stream the ink ejecting nozzles.
There is a further need in a cleaning solution that would not require special sealed compartments or vacuum for residue removal. A cleaning solution that could be easy portable from one print head shape to a print head having a different shape of width or array length.